Depressed persons commonly experience decreased sexual drive, reduced sexual activity, and diminished ability to achieve orgasm. Depressed men also sometimes report changes in erectile function. Clinical experience suggests that such changes are reversible upon recovery from depression. However, it is unclear if diminished sexual interest and function in depressed persons are simply secondary to affective and motivational changes (i.e., dysphoria and more generalized loss of interest) or whether objective biological correlates of altered sexual neurophysiology also are present. Currently, measurement of nocturnal penile tumescence (NPT) is used in clinical practice to assess disorders of decreased sexual function in men. It is widely held that diminished NPT signifies irreversible impotence of an organic etiology (usually associated with peripheral vascular or neuropathic disease). Conversely, psychogenic forms of sexual disturbance are frequently associated with normal NPT profiles. Given the high frequency of disturbances of sexual drive and altered sexual behavior in major depression, as well as the paucity of published data on NPT in depressed men, it is both timely and desirable to test the hypothesis that major depression in men is associated with diminished NPT. Examining this hypothesis also will test the widely held assumption that diminished NPT specifically indicates irreversible impotence, and will establish empirically the incidence of various forms of sexual dysfunction in depressed men. Subjects for this research will be 75 men aged 20-60 meeting SADS/RDC for nondelusional major depression; and 75-aged-matched normal controls. Depressed subjects will represent a cross-section of the male patients assessed and treated at Western Psychiatric Institute and Clinic, including recurrent unipolar, bipolar, melancholic, nonendogenous and "double" depressive subtypes. Following a two-week drug-free assessment phase, a three-night sleep tumescence protocol will be carried out. NPT parameters will be compared between depressives and controls using both univariate and multivariate statistical contrasts. Within the group of depressives, the impact of depressive severity, selected EEG disturbance, and clinical subtype of depression on NPT will be studied.